Alkanesulfonyl chlorides (also known as alkyl sulfonyl chlorides) are known for their utility in imparting functionality into various compounds or as intermediates to modify various compounds, including pharmaceuticals, agricultural chemicals, photographic chemicals and the like, in order to increase their efficacy, to protect sensitive functional groups during certain processing steps, or to improve the recovery and purity during isolation procedures.
Alkanesulfonic acids (also known as alkyl sulfonic acids) are known for their utility as acids and as solvents or catalysts for the preparation of a wide variety of compounds, including pharmaceuticals, agricultural chemicals, photographic chemicals, chemicals for the electronics industry and the like.
A number of prior-art methods are known for preparing alkanesulfonyl chlorides, particularly methanesulfonyl chloride, and alkanesulfonic acids, particularly methanesulfonic acid, but such prior-art methods have a number of disadvantages.
In U.S. Pat. No. 3,626,004 and in British Patent Specification No. 1,350,328, assigned to the same assignee as the present invention, R. M. Guertin discloses the continuous preparation of alkanesulfonyl chlorides and alkanesulfonic acids, respectively, by the reaction of chlorine with alkanethiols or dialkyl disulfides in an aqueous concentrated hydrochloric acid medium. In Japanese Pat. No. 7720970, a continuous process is disclosed for the preparation of methanesulfonyl chloride by reacting methanethiol with chlorine in aqueous hydrochloric acid. In U.S. Pat. No. 3,993,692, S. L. Giolito discloses the continuous preparation of methanesulfonyl chloride by reacting methanethiol and chlorine in saturated aqueous hydrochloric acid containing dispersed methanesulfonyl chloride in an agitated, baffled columnar reactor.
In U.S. Pat. No. 4,280,966, F. Hubenette discloses the batchwise or continuous preparation of alkanesulfonyl chlorides by reacting an alkanethiol or dialkyl disulfide with chlorine and water using the desired alkanesulfonyl chloride as the reaction medium. In European patent publication No. 0040560 and French patent publication No. 2,482,591, H. Gongora describes the continuous preparation of alkanesulfonyl chlorides by reacting chlorine with a stable emulsion of a dialkyl disulfide in water or aqueous hydrochloric acid, which is preformed in a separate mixing vessel with vigorous mechanical agitation.
Each of these methods has the disadvantage that large quantities of hydrogen chloride are produced as a by-product of the reaction according to one of the following general equations: EQU RSH+3Cl.sub.2 +2H.sub.2 O.fwdarw.RSO.sub.2 Cl+5HCl EQU RSSR+5Cl.sub.2 +4H.sub.2 O.fwdarw.2RSO.sub.2 Cl+8HCl EQU RSH+3Cl.sub.2 +3H.sub.2 O.fwdarw.RSO.sub.3 H+6HCl EQU RSSR+5Cl.sub.2 +6H.sub.2 O.fwdarw.2RSO.sub.3 H+10HCl
Thus, five and six moles of hydrogen chloride are produced for each mole of alkanesulfonyl chloride and alkanesulfonic acid formed, respectively, when an alkanethiol is used as the feed, and four and five moles of hydrogen chloride are produced for each mole of alkanesulfonyl chloride and alkanesulfonic acid formed, respectively, when a dialkyl disulfide is used as the feed. Disposal of this large amount of by-product hydrogen chloride presents a severe problem both from economic and environmental considerations.
Another problem associated with the preparation of alkanesulfonyl chlorides by reacting alkanethiols or dialkyl disulfides with chlorine is the formation of undesirable side-products arising from the chlorination of the alkyl side-chain. This problem becomes particularly serious in the preparation of alkanesulfonyl chlorides in which the alkyl side-chain contains two or more carbon atoms.
Production of alkanesulfonyl chlorides by the sulfochlorination of alkanes, which consists of irradiating a mixture of the alkane, sulfur dioxide and chlorine to stimulate the reaction, reduces the amount of by-product hydrogen chloride by 80% according to the following general equation: ##STR1## Sulfochlorination processes have been described in U.S. Pat. Nos. 3,147,303 and 3,458,419, German published application Nos. 2,123,449, 2,217,530, 2,459,159 and 2,805,441, Belgium Patent No. 820,662, German Patents Nos. 147,844, 149,513, 157,702 and 160,830, Russian Patent Nos. 516,683 and 772,106, French published patent application No. 2,575,468 and European published patent application No. 194,931. Although optimization of the alkane/SO.sub.2 /Cl.sub.2 feed ratios has improved the yield of alkanesulfonyl chloride and minimized the production of unidentified "Heavy" by-products, sulfochlorination processes have several disadvantages:
1. Low normal alkanesulfonyl chloride yields; PA0 2. Substantial contamination of the terminal alkanesulfonyl chloride product with non-terminal alkanesulfonyl chlorides when the alkane used as the feed contains three or more carbon atoms; PA0 3. Considerable conversion of the alkane to chlorinated alkanes which increases purification costs and wastes raw materials; and PA0 4. A requirement for highly pure alkane feeds to minimize contamination of the desired alkanesulfonyl chloride product with other alkanesulfonyl chlorides.
In European published patent application No. 194,931, despite substantial improvements, J. Ollivier reported yields of methanesulfonyl chloride of only 75% by the sulfochlorination of methane and that 18% of the methane which reacted was converted to chlorinated methanes. Ollivier obtained somewhat higher alkanesulfonyl chloride yields using propane and butane feeds, but 34% and 43% of the product, respectively, consisted of the 2-sulfonyl chloride isomer. In each case formation of these undesired side-products necessitates purification of the product alkanesulfonyl chloride. In addition, the sulfochlorination method of Ollivier produces only alkanesulfonyl chlorides and production of alkanesulfonic acids requires additional processing steps.
Alkanesulfonic acids have been produced without any attendant production of hydrogen chloride by several different methods: sulfoxidation of alkanes; catalyzed air oxidation of alkanethiols and dialkyl disulfides; catalyzed hydrogen peroxide oxidation of alkanethiols and dialkyl disulfides; and anodic oxidation of dialkyl disulfides. The methods are illustrated by the general equations below. ##STR2##
Sulfoxidation processes have been disclosed in U.S. Pat. Nos. 3,260,741, 3,372,188, 3,413,337, 3,481,849, 3,485,870, 3,658,671, 3,682,803, 3,743,673, 3,926,757, 3,956,371 and 4,643,813, in German publication patent application Nos. 2,019,313, 2,118,363 and 2,924,427, in French published patent applications Nos. 1,531,897, 1,536,649 and 2,102,540, in British Patent Specification No. 1,194,699, in Japanese Patent Nos. 72/7777 and 84/204168, and in European Patent No. 194,201. All of these processes share one serious problem: co-production of very large quantities of sulfuric acid; typically, one mole of sulfuric acid for every 2-4 moles of alkanesulfonic acid. Removal of the by-product sulfuric acid from the alkanesulfonic acid is difficult and is the subject of several patents including German published patent application Nos. 2,014,783, 2,855,849, 3,048,058, 3,325,516, 3,325,517 and 3,412,844. However, none of these patented processes is able to reduce the sulfate content below 10,000 ppm by weight, which is too high for certain electrochemical applications.
In addition, sulfoxidation shares some of the disadvantages of sulfochlorination processes; specifically, poor selectivity for the terminal carbon with alkanes containing three or more carbon atoms, multiple sulfonation, a requirement for highly pure alkane feed to minimize contamination of the desired alkanesulfonic acid with other alkanesulfonic acids, and the fact that sulfoxidation produces only alkanesulfonic acids and is not suitable for production of alkanesulfonyl chlorides.
Catalyzed air oxidation of alkanethiols and/or dialkyl disulfides to alkanesulfonic acids has been described in U.S. Pat. Nos. 2,489,316, 2,489,317, 2,727.92,0 and 3,392,095. In all cases, the catalyst is a nitrogen dioxide (NO.sub.2 or N.sub.2 O.sub.4). Although catalyzed air oxidation is highly selective and produces much less sulfuric acid than does sulfoxidation--typically 1-2 percent by weight in the crude alkanesulfonic acid--the sulfuric acid levels are still too high for electrochemical applications. Moreover, the catalyzed air oxidation of alkanethiols or dialkyl disulfides produces only alkanesulfonic acids and is not capable of producing alkanesulfonyl chlorides.
Catalyzed hydrogen peroxide oxidation of alkanethiols and/or dialkyl disulfides has been disclosed in French published patent application No. 1,556,567, in German published patent application Nos. 2,504,201, 2,504,235 and 2,602,082 and in U.S. Pat. Nos. 3,509,206, 4,052,445 and 4,239,696. The catalyst used is either an ammonium or alkali molybdate or tungstate or the alkanesulfonic acid itself. Nielsen (U.S. Pat. No. 3,509,206) reported that the level of sulfuric acid in the crude 70 percent by weight methanesulfonic acid produced by hydrogen peroxide oxidation of methanethiol or dimethyl disulfide was 0.37 percent by weight which is 10-20 times higher than may be tolerated in electrochemical applications. In addition, this method produces only alkanesulfonic acids and is not capable of producing alkanesulfonyl chlorides.
Anodic oxidation of dialkyl disulfides in an aqueous solution of the corresponding alkanesulfonic acid was disclosed by B. K. Brown in U.S. Pat. No. 2,521,147. This process is economically unattractive because of the low current densities required to achieve reasonable current efficiencies (20 milliamperes/cm.sup.2 to achieve 80% current efficiency) and because of the large amount of sulfuric acid co-product produced. In a direct current electrolysis Brown reported that the alkanesulfonic acid to sulfuric acid molar ratio was 3:1 with a current efficiency of 80%. Electrolysis using alternating current produced only one-fourth the amount of sulfuric acid as was produced using direct current, but the current efficiency using alternating current was only 17%. In addition, the anodic oxidation method is capable of producing only alkanesulfonic acids and not alkanesulfonyl chlorides.
In Russian Patent No. 358,313 A. P. Tomilov discloses the preparation of 2-chloroalkanesulfonyl chlorides (RCHClCH.sub.2 SO.sub.2 Cl) by the batchwise electrolytic oxidation of di-2-chloroalkyl disulfides (RCHClCH.sub.2 SSCH.sub.2 CHClR) in an aqueous concentrated hydrochloric acid medium at 10-18 degrees Centigrade. Although this method circumvents the disadvantageous formation of large quantities of by-product hydrogen chloride, the yields of the desired alkanesulfonyl chloride product are only 70% to 80%. More importantly, the current efficiency, which is an important economic consideration, is low (only 38% to 41%), and this method is limited to production of 2-chloroalkanesulfonyl chlorides.
None of these reported prior-art methods for the production of alkanesulfonyl chlorides or alkanesulfonic acids has the advantages of the method of the present invention.